Thermoplastic matrix composites are processed by first heating the solid resin to flow temperature, at which time the flowing plastic can be formed to the desired shape, and then chilling the formed material to set it. In a continuous reinforced thermoplastic laminating operation, simultaneous heating and application of pressure, or cooling and application of pressure, or any sequence of these can be applied to the laminate as required.
With a common use of polymer or thermoplastic laminated sheets in many structural applications for automotive components such as bumpers, instrument panels, seat and body panels, and further use in a non-automotive application, such as household and sanitary appliances; the production of fiber reinforced polymer laminates by the use of an automated pultrusion machine for continuous laminating has been well established.
Pultrusion is a primary fabrication process which can be used for making continuous length filament reinforced plastic composites wherein two or more flat layers of material are bonded together. In one known thermoset pultrusion process multiple layers of a fiber roving are pulled from creels impregnated with a solution of resin, monomer, fillers and wetting agents; passed through a preformer where excess resin is squeezed off the roving with precise control for uniformity, and given a final shaping and curing in a heated die. The pulling mechanism located in the process after the curing die causes the roving to be pulled through the processing system. Although the majority of pultruded products are formed from polyester resins reinforced with glass fiber, other fibers such as carbon, aramid, (aromatic polyamide), metal, or hybrid fibers which involved more than one type of fiber have also been used as reinforcements; and such thermoset resin as vinyl ester and epoxy have seen use as a matrix material.
More recently, thermoplastic resins have been used as a matrix material in the pultrusion process. In processing thermoplastic material, the pultrusion process is similar to that for thermoset material, except that the curing concept does not apply and use of a cooling die, which is optional for thermoset materials, is required for thermoplastic processing.
The present invention is primarily concerned with producing reinforced laminated sheets using poly(arylene sulfide) as the matrix material in a pultrusion process. Using poly(arylene sulfide) as the matrix material provides pultruded products which will have advantages over the same products made from other materials such as thermoset plastics, steel, wood or aluminum. The poly(arylene sulfide) products are lightweight, can be designed for the strength and stiffness desired, are non-rusting, are corrosion resistant to numerous chemicals and gases, are electrical insulators and have low thermal conductivity.
Because poly(arylene sulfide) forms a semi-crystalline polymer structure, parts manufactured by the pultrusion process using poly(arylene sulfide) reinforced with glass or carbon fibers have widely varying percentages of crystallinity throughout the laminated sheet. The percentage of crystallinity in a poly(arylene sulfide) laminate varies with the line speed, laminate thickness, reinforcement fiber layers, and temperature profile used in producing the laminated sheet. Accordingly, the percent increase in crystallinity of the pultruded laminate achieved by annealing is highly indicative of the percent improvement in the physical properties. Since higher levels of crystallinity improve the quality of the laminate, any annealing process which can increase crystallinity of the laminate is highly desirable.
In the past, it has been typical to provide on-line annealing for shaped polymer products in pultrusion processes by annealing the shaped product as it is pulled through a heated chamber. In this annealing step, the annealing temperature is achieved by introducing a strong blast of heated air, such as from a hot air welding pistol, into the annealing chamber. The article being annealed is protected from the blast of hot air by directing the blast to impinge on a deflector shield. While the above described method of heating the annealing chamber has provided effective annealing temperatures for various shaped articles, the heating method occasionally causes uneven heating for some articles. Uneven heating is indicated by hot spots found on certain shaped articles, such as flat laminated sheets.
It is a primary object of this invention to provide a thermoplastic laminated sheet having improved physical properties.
It is another object of this invention to provide a laminated sheet having improved structural characteristics wherein the improved structural characteristics are achieved in a safe, simple, economic and expedient manner.
It is another object of this invention to provide improved continuous on-line annealing of a pultruded laminated sheet of fiber strands impregnated with poly(arylene sulfide).